I was reading this: http://en.wikipedia.org/wiki/Demographics_of_Asian_Americans#Asian_American_alone
Group Population, 2000 Population, 2010 Percent change
Chinese 2,564,190 3,535,382 37.9%
Indian 1,718,778 2,918,807 69.8%
Filipino 1,908,125 2,649,973 38.9%
Vietnamese 1,169,672 1,632,717 39.6%
Korean 1,099,422 1,463,474 33.1%
Japanese 852,237 841,824 −1.2%
Pakistani 164,628 382,994 132.6%
Cambodian 183,769 255,497 39.0%
Hmong 174,712 252,323 44.4%
Other Asian, not specified 162,913 238,332 46.3%
Laotian 179,103 209,646 17.1%
How come this happened?
The Census Bureau permits people to report up to 6 races: White, Black, Asian, American Indian or Alaska Native; Native Hawaiian or Pacific Islander; and Other. For Asian, AIAN, and NHOPI, they then ask for further delineation (eg Japanese, Navajo, or Samoan).
The table you referred to is for persons who reported Asian
only. So someone who reported they were Asian: Japanese and White would not be counted in that table. The table to its right includes multi-racial person (it is a bit misleading since it also includes Asian-only person).
If you take the difference between the two, the mixed-race Japanese population increased from 296K to 463K. There has not been large scale immigration from Japan after WWII, the population is not particularly concentrated, and it has not been advantageous to emphasize your Japanese heritage, but rather concentrate on being well educated and being financially successful. So you end up with mixed-race marriages. And some of the migration since WWII has been Japanese women marrying American military, which would make the offspring mixed race.
Some people misidentify as Native Hawaiian. To the extent this is done by Japanese (about 1/4 live in Hawaii), it may undercount persons who are Japanese only (the Japanese population is large enough in Hawaii to permit marriage within the community).
The census also does not count only US citizens, or even permanent residents. Rather it counts usually resident, which would only exclude a few diplomats. Someone working for Toyota or Nissan or Honda at an American auto plant, will be reported in the census, and the same would be true for Japanese students attending college. These groups may have declined with the static Japanese population, and mediocre economy, and some will have assimilated and added one or two children to the mixed-race population.